Compressor



J 22, 1937. E; A. STALKER ,08 2

COMPRESSOR Filed June 5, 1953 2 Sheets-Sheet 1 ZAuM MMM June 22, 1937,

C. I CO;

E. v A. STALKER COMPRESSOR- med June 5, 1953 2 Sheets-Sheet 2 26 H6, we

' IWNG 3 MENTOR Patented June 22, 1937.

connssoa Edward A. Stalker, Ann Arbor, ch. Application June 5, 1933,Serial No. 674,342

10 Claims.

concerned'wlth the energization of the boundary- 10 layer on the bladesand on the casing or structure surrounding the blades. It also relatesto the general use of the blades to energize the boundary layer on thecasing wall. In contradistinction application Serial No. 10,408 relatesl5 to the use of the impeller of a plurality of impellers to energizethe boundary layer on the conduit conducting fluid from one impeller tothe other.

Fans are designed so that the blades operate with true angles of attackcorresponding to the greatestratio of lift to drag on the blade section.This means that the lift.coefllcient and the angle is small because themaximum ratio of lift to drag occurs at small values of the lift andangle.

25 The chief reason that the maximum ratio oflift to drag occurs atsmall angles is that the induced drag increases as the lift squared. Theinduced drag, as is well known, arises because of the tips which permita vortex system to form.

30 The lift of a wing is given by L=C;,' A 1) where C1. is the liftcoefficient, A is the area, p is 35 the mass density of the air and V isthe wind velocity. Since the lift is proportional to the liftcoefiicient it is best to speak in terms of 01. be-

cause it is independent of the density, area and velocity.- In a likemanner the total drag of a 40 wing 18 D=Cp'' The drag may be separatedinto two parts, the induced drag due to the finiteness of the span,

45 and the profile drag due to the air friction. That is,

' v n=(c.-+ m

where and R is the aerodynamic aspect ratio.-

Zn my fans I provide a tip shield at the ends of the blades which partlystops the formation of the tip vortices. They will continue to form inpart because the friction of the air with the surface of the shielddissipates some of the kinetic energy of the fluid as heat. Since thedynamic pressure of the fluid is equal to the kinetic energy. 5 there isa loss of dynamic pressure which if present would prevent the air ofgreater pressure a about the blade from flowing into the low pressureregion near the blade surface and forming a vortex. Finally, by addingenergy to the layer -of fluid adjacent the surface of the tip shield Iprevent entirely the formation-of the tip vortex. The layer of fluidadjacent the surface of a body is called the boundary layer.

The elimination of the induced drag makes it possible to use liftcoefficients, as high as 5' for the blade sections economically; andvalues still higher if pressure and rate of rotation are more importantthan the efficiency. An ordinary wing, has a maximum lift coefllcient ofabout 1.5 so that it is necessary to provide special blades to attain avalue 01.:5. High lift coemcients are obtainable through alterations inthe boundary layer. s

The construction'to obtain the elimination of the induced drag andcreate high values of Cr. will be described in detail in connection withthe drawings.

It is customary to refer to blades following helical paths in air asairscrews. For fluids generally. the term fluidscrew is used herein. Thelength of a blade is the length measured at right angles to the relativefluid flow.

In view of the foregoing the objects of this invention may be describedbroadly as a means of improving the efficiency of fluidscrews, vanerotors, and rotary means of pumping by ensuring a smooth flow about theelements. Control of the boundary layer is used to accomplish thiseffect. The same means also makes possible the attainment of many timeshigher pressures than were heretofore possible with similar devices. Iattain these objects by the constructions illustrated in theaccompanying drawings in which- Figure 1 pertains to the theory offluidscrews and indicates the importance of the lift coemcient and theratio of lift to drag.

Figure 2 depicts the characteristics of two types of blade sections,sometimes called wing sections or airfoil sections.

Figure '3 describes the important geometric parameters in airfoilsections.

Figure 4 shows an airfoil section to obtain high values of 01..

insurer is an axial view or a fluidscrew with a peripheral ringshielding the blade tips; Figure 6 is a side view of this combination.Figure 7 is a fragmentary section of the fluidscrew and ring taken alongthe line 1-1 in Figure 5. Figure 5 7a is a fragmentary section of thering or shield taken along the line 1a--'la in Figure 7. Figure 8 is afragmentary view of the blade and ring at their junction.

Figure 9 is a longitudinal section of a screw 10 encased in a tube toconvert the velocity head to a static head. Figure 9a is a cross sectionof a. tube of Figure 9along the line 9a9a.

Figure 10 is a fragmentary section along the line lll|0 in Figure 9.

Figure 11 is a longitudinal section through a fan and tube andillustrates a mode of removing the boundary layer from an expansion tubeso that a large diverging angle 6 may be used. Figure 12 illustratesanother form of the tube for the same purpose and depicts in fragmentarylongitudinal section the relation of thefan and tube to a source offluid pressure such as the cylinder of a fluid engine shown in Figure12a. Figure 12a illustrates in fragmentary section a two cycle gasengine.

In Figure 1 an element I of the blade at radius r is shown. It has a.peripheral velocity or relative to the air. The relative axial velocityis v. The magnitude and true air direction relative to the blade is thengivenby V. The angle of at- 40 file coefficient Cor.

Figure 2 shows the plots of Cr, Cu and CD? against angle of attack fortwo wings whose airfoil sections are shown in Figures 3 and 4. Wingv 2has a section without means to energize the I boundary layer while wing3 is equipped with a slot through which a jet may be discharged toenergize the boundary layer. Figure 3 also defines the geometricproperties of any section. The mean camber line is indicated by 4 andits maximum ordinate is indicated by Ymax which may be expressed as afraction H of. the chord C. The ordinate is measured from the chord 1line subtending the mean camber line or are. The maximum thickness Ytexpressed as a frac- .tion of c is F. It a line be drawn tm-wgn thetrailing edge and'the mid-point of the mean camher line, this line willrepresent the wind direction for zero lift. It is best to measure allangles from this line because when the angle of attack is zero the liftis then zero. 7

The'reason that the lift reaches a maximum and then decreases is that astagnant layer of air forms on the surface of a wing. This layer iscalled the boundary layer and it is well known in aerodynamics that byadding energy to the layer it may be made to disappear; in which casethe lift continues to increase. If enough energy is added the value of01'. may become as high 0 as 12. Energy must be added as velocitytangential to the wing surface or by drawing the boundary layer into thewing. Thus if fluid is blown out an opening to accomplish boundary layerenergization the opening must be formed to discharge in the direction ofthe n ws s the surface. If the opening is formed to discharge normal tothe surface or forward into the oncoming flow the flow willnotbe-energized but deenergized for there will be no component of velocityadded to the flow in the general direction of its normal movement.Rather the flow will become turbulent and, dispersed in every direction.If the openings have axes normal to the surface, only suction to drawthe boundary locate the openings or slots on the curve itself or so thatthey are followed by an expanse of surface'turning from the surfacewhere they are located.

I use the term slot to indicate an opening elongated in the directiontransverse to the flow across a blade or body surface. A plurality ofopenings distributed in the same direction will be equivalent to a slot.The direction of a slot is the direction of the flow axis or thedirection .of the axis of the slot hole. For blowing to energize theboundary layer the slot axis should be nearly tangent-to the bodysurface and directed to the trailing edge or downstream. edge of a bladeor vane.

Figure 4 shows a wing section 3 with a slot lb through which air isblown. In Figure 2 the characteristics for wing 3 are shown for the samespan as for wing 2 but with the tips of I shielded aid with air blow outthe slot 3b. It is to be noted that the maximum value of Cl. is severaltimes larger for the wing with boundary layer energizati'on than for theplain wing. Also the ratio of lift to drag as indicated by the ratio ofthe coeillcients is several times higher and the maximum value occurs athigher angles and high lift coeflicients. This is a very desirablefeature for the type of pumps here described because it permits theeflicient operation of the blades at higher angles than heretoforeemployed. The fan type of pump then becomes suitable for much higherpressures than before. The improvement in the p perties in Figure 2 isdue to both the boundary layer energization of thewing and'of its tipshield which will, be described subsequently.

The shape of the wing section plays an important role in determining thevalue of the maximum C1. and the amount of energy necessary to energizethe boundary layer. The best results are obtained if the nose of thesection is very blunt and the whole section quite'thick. ;The maximumheight of the mean camber line above the subtending chord should belarge. That is, the value of F should be preferably greater than 15percent; thevalue of B should be greater preferably than 10 percent; thenose radius'should approach one-half the thickness which wouldresultinalargeanglebetweentheradiitothe sides of the nose circle wherethe remainder of the wing curve Joins the circumference.

The characteristics of a fan are practically the as the characteristics'ofthe element of the blade at a radius of two-thirds the maximumradius. In other words, the most important section of a fan is in thevicinity of the two-thirds point so that the forms of the blade sectionson either side of this point are most important. In present-day fans thesections are thin and possessed of less mean camber height than 6 percent. In my fans I prefer to form the central half of the blade so thatthe thickness ratio F is between per cent and 50 per cent and the meancamber value H between 10 per cent and 40 per cent. That is, the wingsections to either side of the two-thirds point on the-radius shouldhave these values. In general the greater the value 15 of H the greaterthe value of F should be. For

instance, with a low value of H near 8 per cent the value of F ispreferably about 15 per cent;

while at large values of H near 40 per cent the 'value of F should benear 50 per cent. The value of H should be low for low pressures andhigh for high pressures for a given rate of rotation.

In present-day fans the value of a is of the order of 6 degrees or less,so that for fans operating with a speed ratio of one between the tipsand the relative Wind, the angle 1: is about 51 degrees. This is thevalue of the angle between the plane of rotation and the zero lift line.In my fans the value of preferably exceeds 55 degrees and may be as muchas 90 degrees.

Figure 5 shows an airscrew with end shield 5 at the tip of the bladesindicated as 3 because they are of airfoil section similar to 3. In thisinstance the end shield is a ring extending about the airscrew. Ifdesired it may extend only a short distance above and below the chord ofthe wing section. The shield would take this form on aircraft sustainingwings. A typical junction between the wing and an end shield is shown inFigures 7 and 8 while Figure 7a shows the cross section of the shield.The blades -3 are hollow and their interior compartments 3a communicatewith the opening 6 into the hub 5b. The compartment 3a also communicateswith the interior of the shield 5. when the fan is rotated there is asuction formed on the back of the blade. In the interior of the bladethe pressure is due to the centrifugal force of rotation plus the impactpressure of the air flow against and entering the opening 6 in the hub.As a consequence of the large difference in pressure between theinterior 3a and the exit of the slot 312, a high velocity jet emergesfrom the slot and energizes the boundary layer on the blade. At the sametime a jet is discharged rearward through the slot I in the shield andenergizes the boundary layer on the shield. Hence the lift of the bladeis continued entirely up to the shield surface and no vortex may beformed.

Since the eillciency of a fan is a maximum for a ratio of inflowvelocity to peripheral velocity equal to unity, it is desirable tolocate the fan at the throat of a Venturi tube 9 as shown in Figure 9 tospeed up the flow through the fan. This flgure is a longitudinal sectionthrough the Venturi tube. The fan blades are indicated by 3 and the tipshield by 5 as before. The shield regarded as a ring carries theprojection in which fits snugly into a depression or groove 9a in theVenturi wall. On the inner surface the ring is slightly curved but formsa smooth continuation of the Venturi wall contour.

The Venturi tube increases the speed of the air at the fan and againexpands the flow to a low velocity and a high static pressure. But theordinary Venturi tube has an expansion segment with an included angle 6equal to 5 to 7 degrees which makes an excessively long tube. It theangle 6 is larger than about 7 degrees, the fluid does not follow thewall contours but streams through a central area in the expansionsegment of the tube with a high loss of energy. The expansion segment ofa Venturi tube or any tube is that part where the walls conducting thefluid enclose a cross sectional area of the flow which is increasing inmagnitude in the direction of the flow. Such a conduit of divergentcross sectional area may be called an expansion tube, a diffuser, or adraft tub'e. These terms are in common use in connection with pumpingmachinery and water turbines. The failure of the. fluid to follow thewalls is due to the boundary layer phenomena described earlier. If theboundary layer is removed from the wall as by suction the stream willfollow the wall. .The withdrawn air may be placed back in the stream ifenergy is added to it or if it is placed at a considerable distance infrom the wall. The stream near the wall will still follow it and thefluid may be expanded in a short tube with an expanding exit evenexceeding 90 degrees.

In Figure 9 I indicate one method of removin the boundary layer from thecritical point where the expansion of the cross section begins. Acircumferential aperture II in the Venturi wall opens into a conduitllencircling the Venturi tube. In the center of the venturi a conduitl2a connects l2 with the hub fairing l3. Figure 9a shows the crosssection of tube i211. Figure Ill which is a section of the fairing alongiii-40 of Figure 9 shows that the interior of the fairing is hollow andhas in its surface a peripheral slot it. Since the slot lies on astreamline body and is located at a more reduced cross section of theventuri than the point i I, there will be more suction at It than H sothat fluid will be removed at I i and introduced into the stream at M.

Figure 11 is a longitudinal section of a Venturi tube and illustratesanother method of energizing the boundary layer at l I. In this instancea compartment i5 is formed in and encircles the venturi and a conduit i6similar to PM leads from the compartment to a stationary hollow hub I!which communicates with the hub inlet 6. -By this arrangement thecentrifugal force in the blades draws the boundary layer from theperipheral aperture i and forces it out the blade and shield openings 3band 1. Thus the fan energizes the blade, the shield and the venturiboundary layers.

It is to be noted also that the fluid which has passed the blade has apressure higher than the fluid ahead of the blade so that the downstreamor compressed fluid is most desirable for use in energizing the boundarylayer on the blade.

Figure 12 shows still another arrangement that will permit very largevalues of the angle 6. The boundary layer is removed at ill by thesuction at the throat of the Venturi tube. The suction is communicatedby the passage II to the peripheral opening i9. Since I8 is' so farremoved from the throat there is an appreciable pressure difference 65between the localities l8 and i9. By this ar- 10 tively small.

'ment 2| by the pipe 22 coming from a pump maintained for this purpose.The jet issuing from 20 has a high velocity and energizes the boundarylayer. It would be economical to maintain a pump for energizing serviceand part of the-fluid could be fed to a central tube 23 which would leadto the blade interior for use in the openings ib and I to which accesswould be gained through the hub entrance 6. The pump could be compara- Iprefer, however, to utilize the waste fluid under pressure that is sofrequently available in industrial plants. As an example of theutilization of waste fluid under pressure, -I show the cylinder 24 of atwo cycle internal com- 15 bustion engine. The piston is 25 and thenormal exhaust port is 26. Just before the piston uncovers the exhaustport 26, a port 21 is uncovered. It communicates by means of the tube 28with a container 28. A check valve 30 keeps the flow in 20 the containerand the latter serves as a means of steadying the flow to the ducts 2iand 23, to both of which 28 may be connected.

I use the term vane as a general term for wing or blade to indicate abody used to direct fluid.

Referring to the blades or vanes of an impeller I use the term upper andlower surfaces to mean the suction and pressure surfaces respectively.

That is, the surface which attacksthe fluid is the pressure surface orlower surface. The surface 30 on the opposite side of the vane is theupper surface. blade.

The structure about the fan or impeller may in general be termed ahousing or casing'as well as a 35 tube. While the forms of the apparatusherein described constitute preferred embodiments of the invention, itis to be understood that changes may be made herein that do not departfrom the scope It is also sometimes called the back of the 40 of theinvention which is defined in the appended claims.

What I claim is: 1. In combination, a rotatable fluidscrew havingblades, a casing to encircle the fluidscrew and 5 conduct a fluid flowthrough the fluidscrew, said casing having an entrance upstream from thefluidscrew to admit fluid and an exit downstream to emit the fluid, anda peripheral slot in the casing side wall to admit a relatively thin jetinto the casing substantially tangentially to its inner surface at alocality substantially upstream of the plane of rotation of the trailingedge of said blades, said jet serving to energize the boundary layer onthe casing between blade tips to maintain a high value of the blade liftnear the tips.

2. Incombination, a fluidscrew bathed by a relative flow of fluid andhaving blades of hollow interior, said blade having a perforated upper60 surface to form an opening in communication with the blade interior,means of causing a flow through said'opening to energize the boundary.layer and create an augmented lift on the fluidscrew, said lift givingrise. to a high induced drag,

65 means to suppress the induced drag comprising an annular tip shieldextending about the blades and having an opening in its inner surfacewith a flow therethrough to energize the boundary layer arising fromsaid relative flow.

7o 3. In a means of blowing, hollow blades whose mean camber maximumordinate exceeds 10% of the chord, and whose thickness is greater thanof the chord a hollow end shield at the blade tips. openings in theupper surfaces of the blades 7 and the inner surfaces of the shields,and means to supply fluid to the openings, said shield being annular andextending around the blade tips.

4. In a compressor associated with a flow of fluid and having hollowvanes which have open-:

ings on their suction-side in communication with their hollow interior,said openings in the vanes tion with the blade interior, said bladehaving a V rearward directed discharge slot in the upper surface incommunication with the blade interior, said slot being succeeded by ablade surface tuming from the flow so as to tend to cause a separationof the flow from the blade surface, said slot havingside wallsoverlapping rearward to direct fluid rearward substantially along thesurface and being extensive radially along a major portion of the radiallength of the blade so as to be suitable for use in energizing theboundary layer, and a source of fluid supply under pressure incommunication with the hub inlet so a fluid jet is dischargeablefrom'the said discharge slot substantialy along the surface to suppressthe tendency to flow separation by boundary layer energization, saidsource of fluid supply being other than the pumped fluid and at apressure substantially higher than said pumped fluid.

6. In combination to form a means of pumping fluid, a fluid impeller, acasing having an entrance said throat portion having a peripheraldischarge opening, a conduit interconnecting the said inlet anddischarge openings, and means to discharge a fluid jet through and alongthecasing wall, said fluid jet issuing into the interior of the casingat a wall locality situated between the said inlet and dischargeopenings.

7. A fluid compressor comprising in combination a casing containingfluid, a hollow rotatable blade to discharge fluid into the casing tocompress the fluid therein and having a slot in the upper surface incommunication with the blade interior, said slot extending radiallyalong a major portion of the blade length and having sides overlappingrearward to direct fluid rearward substantially along the blade surfacefor use in energizing the boundary layer on the blade, and conduit meansto convey fluid from a region of compressed fluid downstream from saidblade to the blade interior for discharge from said slot to ener gizethe boundary layer on the blade.

s. A tube having diverging walls, a pumping past itself, walls forming acasing to receive the impelled fluid from maniacs and guide the fluiddownstreamsaidcasinghavinganinletandan 2,084,462 exit for said main flowand a wall surface turning from the main flow'and a slot in said wallfor the energization of the boundary layer formed by the contact of thefluid with the wall surface, said blade having an opening in the surfaceat a substantial distance from the said axis and in communication withthe blade interior, and a conduit means communicating between the slotand the opening in the blade surface so that centrifugal action of thefluid in the blade induces a flow through said slot to energize theboundary layer on the casing wall.

10. In a vane blower, a vane, a hollow shield at EDWARD a. STALKER. m

